Phthalocyanine compounds which were originally developed as pigments are thermally and chemically stable. Besides, their solubility and absorption property can be changed with their structural characteristics by introducing various substituents at the outer structure of them. Therefore, phthalocyanine compounds are being widely used in various uses which require thermal and chemical stability, especially, in various electronics industry fields, according to the recent explosive growth of electronics industry, for example, in uses such as pigments applied in organic photo conductor for laser print, near-infrared absorption materials for PDP (plasma display), sensitizers for solar cell, and so on.
Especially, according to the recent rapid expansion of the display industry, the usage of near-infrared absorption filter for PDP is sharply increasing, thus, the demand of near-infrared absorption materials is increasing. The near-infrared absorption filter for PDP is used to block the light in the near-infrared light region which is one of various light sources generated from PDP and may cause malfunction of the home remote control. A near-infrared absorption pigment which is used in the near-infrared absorption filter must increase transmittance of the visible light generated from light source and improve color gamut (color reproductivity) of display devices by having superior light absorption property in the region of 800 to 1100 nm and low light absorption property in the visible light region. Also, the near-infrared absorption pigment must have solubility, weather resistance, durability, and so on, for the convenience of process. As the near-infrared absorption pigment, representatively, the above stated cyanine based compounds, nickel-dithionyl based compounds, diimonium based compounds and so on, are known. However, the cyanine based compounds are difficult to be applied actually because of lack of heat resistance, and the diimonium based compounds are not suitable for the near-infrared absorption filter method of coating type which is being used recently in display industry, because of lack of durability to the environment such as moisture. Also, the nickel-dithionyl based compounds are limited in application, because of low solubility, even though they have an advantage of low light absorption property in the visible light region.
On the other hand, the phthalocyanine compounds are superior to other compounds in durability and weather resistance, and can solve the problem of solubility by controlling the substituent of the outer of structure, and can increase light absorptivity rather freely in the most near-infrared light region of 800 to 1100 nm, so that they are known to be suitable for the coating type near-infrared absorption filter method for PDP. However, conventional phthalocyanine compounds for the absorption of near-infrared light have superior photosensitive characteristic mainly in the region of 900 to 1000 nm, but have a disadvantage in that light absorptivity in the visible light region is a little higher than nickel-dithionyl based compounds and so on and color gamut is decreased, Also, the light absorptivity of conventional phthalocyanine compounds is not fully enough in the region of 880 to 920 nm which occupies the largest portion in the near-infrared light generated from the light source for PDP. Therefore, various studies for increasing the light absorptivity in the region of the above stated main wavelength by changing the central metal of phthalocyanine compound or the substituents of the outer of compound structure, have been done. However, in the case that a substituent such as a phenol, a thiophenol, first amine, and so on is introduced, the light absorptivity in the visible light region is increased too and color gamut is decreased, then applications are limited.